Movable windows conventionally utilize various types of locking arrangements for selectively preventing and permitting a sash to move with respect to other sashes or parts of the window assembly. A known technique is to mount a keeper on one sash and a lock on the other sash. The keeper generally includes a spaced downwardly extending locking tab. The lock includes a rotatable cam which has an arcuate cam member having a first free end and a second end remote from the free end. The lock is mounted with respect to the keeper so that in the unlocked condition the cam member is completely within the lock housing thereby permitting free movement of the sash. In the locked condition, however, the cam is rotated so that its free end passes out of the housing and the inner surface or inner side wall of the free end passes behind the inner surface of the keeper locking tab. The rotational movement of the cam member continues until the inner side wall of the free end is sufficiently disposed against the keeper tab to prevent movement of the sash.
The above arrangement conventionally uses a cam member which has an arcuate inner surface for engaging the inner surface of the keeper tab. A disadvantage with such arrangement, however, is that for proper locking there must be precise alignment of the lock and keeper since any misalignment would not permit the proper engagement of the cam member and keeper tab.